Which term best describes the upper boundary between saturated and unsaturated zones in an aquifer?

• A. Phreatic zone
• B. Water table
• C. Infiltration capacity
• D. Baseflow

Answer: (B)

The boundary between the saturated and unsaturated zones is defined by the water table. It marks the surface where pore spaces go from being filled with water (below) to being only partially filled or dry with air above. In an unconfined aquifer, the water table rises and falls with recharge from rainfall and with withdrawals, directly outlining the top of the saturated zone. The term phreatic zone refers to the saturated portion of the aquifer itself, not the boundary, while infiltration capacity is about how quickly surface water can enter the soil and baseflow is groundwater’s contribution to streamflow. So, the water table is the correct description of that upper boundary.